Peripheral heavy-ion collisions below the Fermi energy: The case of 86Kr + 64Ni and 86Kr + 124Sn at 15 MeV/nucleon

AbstraktAbstract

Exploring the reaction mechanisms responsible for the production of neutron-rich nuclides, we undertook a systematic study of the momentum distributions of projectile-like fragments from peripheral collisions of 86Kr at 15 MeV/nucleon with 64Ni and 124Sn. For this purpose, our previous data collected with the momentum achromat recoil separator (MARS) at the Cyclotron Institute of Texas A&M were adopted. The momentum per nucleon (p/A) distributions of the ejectiles are characterized by a quasi-elastic peak just below the projectile velocity and a region at lower velocities corresponding to dissipative events. Two-body kinematics was employed to extract the total excitation energies of these regions. It was found that very neutron-rich isotopes can be probed in these reactions, especially with the heavier target via processes involving proton removal, neutron pickup, or a combination of these, up to a triple charge exchange process observed in the data. The experimental data were systematically compared with calculations employing the deep-inelastic transfer (DIT) model and the constrained molecular dynamics (CoMD) model followed by the GEMINI deexcitation code. The DIT model, phenomenologically treating the sequential exchange of nucleons, offered an overall qualitative description of the experimental momentum distributions, however underestimating the data in the quasielastic part of most of the channels. The CoMD model, based on a fully microscopic N-body approach, offered an overall better description of the majority of the data, whereas, in some cases, it led to overestimation of the quasielastic part of the momentum distributions. The detailed comparison of the model calculations with the experimental data provided valuable insight into the reaction mechanisms in this energy regime, suggesting, apart from independent nucleon exchange, the contribution of target inelastic excitation and direct reaction processes involving neutron and proton pair transfer, cluster transfer, and meson-mediated charge exchange. This work paves the way to a systematic investigation of the mechanisms of multinucleon transfer reactions involving medium-mass heavy ions below the Fermi energy and provides guidance for the production of exotic neutron-rich nuclei.

Exploring the reaction mechanisms responsible for the production of neutron-rich nuclides, we undertook a systematic study of the momentum distributions of projectile-like fragments from peripheral collisions of 86Kr at 15 MeV/nucleon with 64Ni and 124Sn. For this purpose, our previous data collected with the momentum achromat recoil separator (MARS) at the Cyclotron Institute of Texas A&M were adopted. The momentum per nucleon (p/A) distributions of the ejectiles are characterized by a quasi-elastic peak just below the projectile velocity and a region at lower velocities corresponding to dissipative events. Two-body kinematics was employed to extract the total excitation energies of these regions. It was found that very neutron-rich isotopes can be probed in these reactions, especially with the heavier target via processes involving proton removal, neutron pickup, or a combination of these, up to a triple charge exchange process observed in the data. The experimental data were systematically compared with calculations employing the deep-inelastic transfer (DIT) model and the constrained molecular dynamics (CoMD) model followed by the GEMINI deexcitation code. The DIT model, phenomenologically treating the sequential exchange of nucleons, offered an overall qualitative description of the experimental momentum distributions, however underestimating the data in the quasielastic part of most of the channels. The CoMD model, based on a fully microscopic N-body approach, offered an overall better description of the majority of the data, whereas, in some cases, it led to overestimation of the quasielastic part of the momentum distributions. The detailed comparison of the model calculations with the experimental data provided valuable insight into the reaction mechanisms in this energy regime, suggesting, apart from independent nucleon exchange, the contribution of target inelastic excitation and direct reaction processes involving neutron and proton pair transfer, cluster transfer, and meson-mediated charge exchange. This work paves the way to a systematic investigation of the mechanisms of multinucleon transfer reactions involving medium-mass heavy ions below the Fermi energy and provides guidance for the production of exotic neutron-rich nuclei.